Abstract:
Systems and methods for a non-data-aided (NDA) approach to advanced OFDM timing are provided. This approach allows for accurate OFDM symbol timing and synchronization by avoiding inter-symbol interference (ISI) in multipath environments where an earliest arriving signal may not be the strongest signal. The NDA approach may rely on generating and applying a bias correction to a combined correlation result of the multi-path signals.
Abstract:
Systems and methods for maintaining synchronization of repeater networks with Global Positioning System (GPS) signals using phase locked loops (PLLs) and based on generation of predicted control words for controlling local oscillator frequencies is described. The predicted control words can be generated based on performing a linear fit of control words generated over a predetermined duration of time. Phase locked loops with additional false GPS pulse identification and GPS signal loss compensation circuitry can enforce a false pulse count threshold and/or an error threshold. The additional circuitry and prediction of control words can overcome errors in GPS receiver outputs and maintain accuracy of signal timings across single frequency networks using inexpensive local oscillators.
Abstract:
Systems and methods for enabling pre-compensation of timing offsets in OFDM receivers without invalidating channel estimates are described. Timing offset estimations may be sent along with the received OFDM symbols for FFT computation and generating a de-rotated signal output. The timing offset estimation may provide a reference point for dynamic tracking of timing for an OFDM signal and estimated based on an integral value associated with the OFDM signal.
Abstract:
Systems, algorithms and methods for reclaiming unused portions of a satellite broadcast service's bandwidth for new services, utilizing higher performance coding techniques to yield better throughput, are presented. These systems, algorithms and methods achieve the reclaimed bandwidth in a way that is invisible to a legacy receiver, and that does not interfere with its reception of a legacy signal. In one embodiment, new data may be transmitted within a legacy transmission frame, for example within its cluster structure, using the same modulation and synchronization as used for the legacy data. The new data may be inserted into a channel or other subdivision at a head end. In another embodiment, one or more clusters or subdivisions with only new data may be transmitted, using the same modulation and synchronization as the legacy data clusters, but now employing a higher performing FEC and data interleaving structure on those clusters which contain only new data to yield an increase in available throughput. Finally, in a third embodiment, one or more clusters containing only new data may be transmitted, and in said one or more all new data clusters, different modulation and synchronization may be used then that of the legacy data clusters, thus employing a higher performing FEC and data interleaving structure than that of the legacy clusters. Various combinations of these approaches are also presented, as well as a set of novel receivers, or receiver configurations, to implement them and their combinations
Abstract:
Systems and methods for enabling pre-compensation of timing offsets in OFDM receivers without invalidating channel estimates are described. Timing offset estimations may be sent along with the received OFDM symbols for FFT computation and generating a de-rotated signal output. The timing offset estimation may provide a reference point for dynamic tracking of timing for an OFDM signal and estimated based on an integral value associated with the OFDM signal.
Abstract:
Systems, algorithms and methods for reclaiming unused portions of a satellite broadcast service's bandwidth for new services, utilizing higher performance coding techniques to yield better throughput, are presented. These systems, algorithms and methods achieve the reclaimed bandwidth in a way that is invisible to a legacy receiver, and that does not interfere with its reception of a legacy signal. In one embodiment, new data may be transmitted within a legacy transmission frame, for example within its cluster structure, using the same modulation and synchronization as used for the legacy data. The new data may be inserted into a channel or other subdivision at a head end. In another embodiment, one or more clusters or subdivisions with only new data may be transmitted, using the same modulation and synchronization as the legacy data clusters, but now employing a higher performing FEC and data interleaving structure on those clusters which contain only new data to yield an increase in available throughput. Finally, in a third embodiment, one or more clusters containing only new data may be transmitted, and in said one or more all new data clusters, different modulation and synchronization may be used then that of the legacy data clusters, thus employing a higher performing FEC and data interleaving structure than that of the legacy clusters. Various combinations of these approaches are also presented, as well as a set of novel receivers, or receiver configurations, to implement them and their combinations
Abstract:
Systems, methods and apparatus are described to interleave LDPC coded data for reception over a mobile communications channel, such as, for example, a satellite channel. In exemplary embodiments of the present invention, a method for channel interleaving includes segmenting a large LDPC code block into smaller codewords, randomly shuffling the code segments of each codeword and then convolutionally interleaving the randomly shuffled code words. In exemplary embodiments of the present invention, such random shuffling can guarantee that no two consecutive input code segments will be closer than a defined minimum number of code segments at the output of the shuffler. In exemplary embodiments of the present invention, by keeping data in, for example, manageable sub-sections, accurate SNR estimations, which are needed for the best possible LDPC decoding performance, can be facilitated based on, for example, iterative bit decisions.
Abstract:
Systems and methods are presented for transmitting additional data over preexisting differential COFDM signals by modulating existing data carriers with a phase and an amplitude offset. In exemplary embodiments of the present invention, additional data capacity can be achieved for an COFDM signal which is completely backwards compatible with existing satellite broadcast communications systems. In exemplary embodiments of the present invention additional information can be overlayed on an existing signal as a combination of amplitude and phase offset from the original QPSK symbols, applied for each information bit of the overlay data. With two additional levels of modulation, a receiver can demodulate the information from each of the previous stages and combine the information into a suitable format for soft decoding. The first stage of demodulation will be recovery of overlay data from the amplitude modulated D8PSK. Because other amplitude variations due to multi-path are also expected, the data gathered from the FFT in the receiver must be equalized to the channel conditions. After channel equalization has been performed, soft overlay data can then be derived from the distance off the unit circle. In order to recover the phase modulated overlay data, the equalized symbols must first be differentially demodulated and corrected for any common phase error offset. After common phase removal, overlay phase information can be obtained.